Abstract: This paper presents an efficient coarse grain multicomputer (CGM) parallel algorithm for the cost of the optimal binary search tree problem (OBST problem). In the previous best CGM algorithm for this problem, the size of the local memory of each processor is not bounded. And even, in the worst case, its running time reduces to the one of Knuth's sequential algorithm for the same problem, bringing no gain by parallelising OBST. Our CGM algorithm uses Knuth's sequential algorithm for local computations to perform in time as well as the best previous CGM algorithm. Moreover, each processor can process at most two blocks and thus avoid the severe drawback raised above of the previous work.